1. Field of the Invention
An elastic universal coupling according to this invention is installed to, for example, an automotive steering apparatus to transmit the movement of the steering shaft to the steering gear.
2. Related Background Art
The automotive steering apparatus is constructed, for example, as shown in FIG. 5.
The movement of a steering wheel 1 is transmitted to a steering gear 4 through a steering shaft 2 and a connecting rod 3, and this steering gear 4 steers the wheels.
The steering shaft 2 and an input shaft 5 for the steering gear 4 are usually not coaxial with each other. For this reason, the connecting rod 3 has been conventionally provided between the steering shaft 2 and the input shaft 5, and both ends of the connecting rod 3 are connected with the end of the steering shaft 2 and that of the input shaft 5 through universal couplings 6, 6 respectively in order to transmit torque between the steering shaft 2 and the input shaft 5.
The universal coupling 6, which is installed in such a power transmission mechanism, etc., is provided with a vibration-proof mechanism so as not to so as transmit vibration of the wheels to the steering wheel 1.
As examples of an elastic universal coupling with the vibration-proof mechanism, those as specified in Japanese Utility Model Application Laid-Open No. 63-69077 and U.S. Pat. No. 4,983,143 are known, and the former is shown in FIG. 6.
In FIG. 6, a yoke 7 is bifurcated by press molding metallic plate having sufficient rigidity, and a pair of circular holes 8, 8, which are coaxial with each other, are provided at the tip ends (right ends in FIG. 6) of the yoke 7. A second yoke (not shown in FIG. 6) is coupled to the yoke 7 by a cross shaft (not shown in FIG. 6) which is pivotally connected to the yoke 7 at holes 8, 8 and also to the second yoke. It is thus possible to freely transmit a rotating force between the second yoke (not shown) and the yoke 7.
A shaft 9 has one end secured by welding to the base (left) end of the yoke 7, and a second end having a serrated portion. An inner cylinder 13, which forms an elastic member 12 together with an outer cylinder 10 and an elastic body 11, is fitted to the serrated portion. The outer cylinder 10 is cylinder 14 which will be crushed if a strong force in the axial direction is applied, and another shaft 15 is secured to the other end of the combined cylinder 14.
In the elastic universal coupling described in the above-mentioned Japanese Utility Model Application Laid-Open No. 63-69077, even if vibration travels from the wheels to the shaft 15, this vibration will be absorbed by the elastic body 11 of the elastic member 12 owing to the above-mentioned construction. Therefore, the vibration will not travel to the shaft 9 connecting with the steering wheel 1. If the shaft 9 is strongly pushed due to a collision, the combined cylinder 14 will be crushed to prevent the steering wheel 1 connecting with the shaft 9 from being thrust up.
However, in the case of a conventional elastic universal coupling constructed as mentioned above, the length in the axial direction has to be long because the yoke 7 is connected with the elastic member 12 through the shaft 9.
For this reason, if the length of a portion for installing the elastic universal coupling cannot be made sufficiently long, the conventional coupling cannot be used.
Also since the diameter of the elastic body 11 to be fitted to the outside of the shaft 9 through the inner cylinder 13 is small, the torsional rigidity of the elastic body 11 is not always adequate, thus creating problems with controllability and stability.
To improve the controllability and stability, it is possible to increase the rigidity of the elastic body 11. However, when the hardness of the elastic body (rubber) 11 is increased for this purpose, the vibration damping performance becomes insufficient. To make the elastic body 11 comparatively soft and yet increase the rigidity thereof, it is conceivable to make the diameter of the elastic body 11 large. But, in the case of the above-mentioned conventional construction, the diameter of the elastic body 11 could not be made sufficiently large to provide adequate controllability, stability, and vibration damping performance.
In this respect, the invention specified in the above-mentioned U.S. Pat. No. 4,983,143 has also the same problem.